1

2

Dr Stefan Hessa), Prof Vic Hanbyb)

a) Solar Thermal Energy Research Group (STERG)

Stellenbosch University

b) De Montfort University Leicester, UK

Stationary Booster Reflectors for Solar

Thermal Process Heat Generation

3

• Stationary Concentrators

• Efficiency Tests and Output Simulation

• Monitoring of a Pilot Plant

• Marginal Costs

• Summary and Outlook

4

External Compound Parabolic Concentrators (CPC´s)

Very common: CPC´s for evacuated tube

collectors (Weiss and Rommel 2008)

External CPC for flat evacuated SRB collector

(Picture: Intersolar Munich 2011)

5

Flat booster reflectors

Flat-plate collector

field with corrugated

aluminium sheet

booster reflectors

in Östhammer,

Sweden.

Picture: Karlsson,

cp. (Rönnelid and

Karlsson 1999)

6

Gbt = Beam irradiance (Aperture 5.72°)

Gst = Diffuse from sky

Grt = Diffuse from ground

RefleC-Collector at pilot plant Laguna

(positive transversal incidence angle

indicated)

Horizon

anisotropicisotropic

s

Horizon

anisotropicisotropic

s

7

• Stationary Concentrators

• Efficiency Tests and Output Simulation

• Monitoring of a Pilot Plant

• Marginal Costs

• Summary and Outlook

8

Measured efficiency curves of RefleC and its flat-plate

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

25 40 55 70 85 100 115 130 145 160 175 190 205

Co

llecto

r eff

icie

ncy η

┴[

-]

Mean fluid temperature Tf [ °C ]

Flat-plate LBM 4 GF (glass + foil)

RefleC 6 (LBM 4 GF)

Ambient temperature

Global irradiance

9

Distribution of diffuse

irradiance for a slightly

covered sky

k = 0.95, kt= 0.35

Distribution of diffuse

irradiance for a clear sky

k = 0.25, kt= 0.75

Diffuse distribution from Brunger model (48 classes)

k = fraction

of diffuse

kt= clearness

index

10

Three modes for diffuse-IAM:

• Mode 1: Anisotropic for sky (dynamic),

isotropic for ground (once per sim)

• Mode 2: Isotropic for sky (once per

sim), isotropic for ground (one per sim)

• Mode 3: Manual input of one

hemispheric IAM for isotropic diffuse

Gbt = Beam irradiance

Gst = Diffuse from sky

Grt = Diffuse from ground

Horizon

anisotropicisotropic

s

Hess, S. and Hanby, V. I.

(2014). Collector

Simulation Model with

Dynamic Incidence Angle

Modifier for Anisotropic

Diffuse Irradiance. Energy

Procedia 48(0): 87-96

11

0

200

400

600

800

T_in = 40 °CMode 3

(isotropic)

T_in = 40 °CMode 1

(anisotropic)

T_in = 120 °CMode 3

(isotropic)

T_in = 120 °CMode 1

(anisotropic)

Co

lle

cto

r g

ain

[k

Wh

/ (

m2fp

a)]

Additional gain reflector

Flat-plate LBM 4 GF

+ 8 %

+ 3 %

+ 26 %

+ 66 %

Annual output of RefleC 6 GF (blue plus red) and its receiver LBM 4 GF (blue) in Würzburg. Output

increase by booster is 20 % at constant Tin = 40 °C and 87 % at Tin = 120 °C

12

• Stationary Concentrators

• Efficiency Tests and Output Simulation

• Monitoring of a Pilot Plant

• Marginal Costs

• Summary and Outlook

13

Reference flat-plates (glass-foil, front) and new RefleC-collectors (back)

Flow

collector field

System

14

storage1000 l

120 °C

3 bar

stora

ge

2x1000l

110 °C

3 bar

Boiler feed-

water

90 °C – 110 °C

4,6 m³ / d

Boiler makeup-

water

20 °C - 90 °C

3 m³ / d

Washing

machines

20 °C - 60 °C

1 m³ / d

RefleC

2 x

20,2 m²

Flat-plates

(glass + foil)

16,2 m²

Tmax = 130 °C

psys = 6 bar

Stagnation cooler

Primary

storage

Secondary

storages

300l

60°C

Fig: Simplified system concept of the RefleC pilot plant

• Increased temperatures for solar loop and storage

• Three thermal loads on process- and supply level

15

Additional gains over 16 months

0

1

2

3

4

5

6

Jul10

Aug10

Sep10

Oct10

Nov10

Dec10

Jan11

Feb11

Mar11

Apr11

May11

Jun11

Jul11

Aug11

Sep11

Oct11

Su

m p

er

avera

ge d

ay [

kW

h / (

m2fp

d)]

Global irradiance G_t(aperture-specific)Gain flat-plate (aperture-specific)Gain RefleC (per flat-plateaperture)

+ 39.1 % all temperatures

+ 78.1 % T ˃ 80 °C

16

• Stationary Concentrators

• Efficiency Tests and Output Simulation

• Monitoring of a Pilot Plant

• Marginal Costs

• Summary and Outlook

17

Parameters:

• Field simulations: additional gain boosters Würzburg = 126.0 kWh/m2

Seville 212.5 kWh/m2 flat plate

• Monitoring: system efficiency 0.86 (i.e. 108 kWh/m2fp supplied in Wb)

• Conventional heat 0.06 EUR/kWh, aim for solar heat 0.04 EUR/kWh

• Lifetime 20 years, interest rate 4 %, no costs for maintenance & operation

Results:

• Investment in Würzburg max. 40 EUR/m2 of booster (= 480 EUR/LBM fp),

amortization static: 9 years

• Seville: 67 EUR/m2 booster (= 804 EUR/LBM); amortization 5.4 years

Kinv = Ksol ⋅ Qsol

fa

Calculated according to VDI 6002, 2004

18

• Previous research undervalued increase by boosters

• Increase in annual gain largely independent of collector working

temperature process heat!

• Cost/performance ratio increases with higher overall irradiation.

• Marginal reflector costs in regions with higher irradiance to be

determined (e.g. South Africa Solar PACES)

• RefleC-boosters for other stationary collectors

• Comparison to other collector types for various applications

Dissertation available: www.reiner-lemoine-stiftung.de

19 visit us: concentrating.sun.ac.za

ACKNOWLEDGEMENTS:

CONTACT DETAILS:

Dr Stefan Hess

Solar Thermal Energy Research

Group (STERG)

Stellenbosch University

South Africa

stefanhess@sun.ac.za

+27 (0)21 808 4016

20

5 % Hydro + RE

6 % Fuel + others

4 % Nuclear

85 % Coal

SATIM 2014. Assumptions and Methodologies in the South African TIMES (SATIM) Energy Model. Energy

Research Centre, University of Cape Town: http://www.erc.uct.ac.za/Research/esystems-group-satim.htm

Blackdotenergy 2015. Commercial installations in SA: http://www.blackdotenergy.co.za

Hess, S. 2014. Low-Concentrating, Stationary Solar Thermal Collectors for Process Heat Generation.

Dissertation. Leicester University. www.reiner-lemoine-stiftung.de

Hess, S. and Hanby, V. I. (2014). Collector Simulation Model with Dynamic Incidence Angle Modifier for

Anisotropic Diffuse Irradiance. Energy Procedia 48(0): 87-96

IEA 2012. IEA Technology Roadmap Solar Heating and Cooling. International Energy Agency. Paris. URL:

http://www.iea.org/publications/freepublications/publication/

Solar_Heating_Cooling_Roadmap_2012_WEB.pdf

IRENA (International Renewable Energy Agency) 2015. Solar Heat for Industrial Processes. Technology Brief.

Available from www.irena.org/Publications [Accessed 1 April 2015].

Lauterbach, C., Schmitt, B., Jordan, U. and Vajen, K. 2012. The potential of solar heat for industrial processes in

Germany. Renewable and Sustainable Energy Reviews 16(7): 5121-5130.

Rönnelid, M. and Karlsson, B. (1999). "The Use of Corrugated Booster Reflectors for Solar Collector Fields."

Solar Energy 65(6): 343-351.

21

Primary storage tank (left), two parallel secondary storages (center), expansion vessel

and the hot water storage for the washing machines

22

Fig.: Screenshot from OptiCad

23

theta_t = 0°

Aap

24

theta_t = 10°

Aap

25

theta_t = 20°

Aap

26

theta_t = 25°

Aap

27

theta_t = 30°

Aap

28

theta_t = 40°

Aap